Abstract：High-resolution turbulence simulations were performed for an X-51A-like aircraft model to investigate its complex unsteady separation flow caused by high angle of attack conditions. The calculation is based on delayed detached-eddy simulation (DDES) methodology under high order. Flow Mach number is 2.5, and the angle of attack is 10°. In this paper, separation flow phenomenon, separation flow induced aerodynamic characteristic variation law and pressure fluctuation features are analyzed. Especially, the distribution of wall pressure fluctuation and the spectrum characteristics of the monitors are mainly studied. The result shows that lateral edges of the model lead to a large number of separated vortices when the aircraft flies under large angle of attack, which cause strong interference with the vertical tail rudder. The interfered tail rudder exhibits obvious nonlinear and unsteady aerodynamic properties. In addition, the presence of separation vortices also leads to a significant increase in pressure fluctuation on the aircraft wall, especially on the leading edge of tail rudders. The power spectrum density of pressure shows that low frequency and high amplitude fluctuation of 200-300 Hz may cause structural damage.